BGDB Practical - Sexual Differentiation

Introduction

This practical will introduce the topic of sexual differentiation during development through a series of online resource pages.

Aim: This practical is an introduction to the earliest events in Sexual Differentiation.

Key Concepts: primordial germ cell, sex chromosomes, gonad, internal genitalia, external genitalia, ovary, testis, puberty, hormonal changes, gametogenesis, genital abnormalities (DSD).

Background

Historic Gonad Images

Two key systems, neural and reproductive, develop over an extended period from the early embryo to puberty and the emerging adult. The genital system is closely linked developmentally to the urinary system, often called the urogenital system. This practical will therefore cover early development of both system.

In understanding embryonic sexual development, think of a cascade of sequence dependent events that transform indifferent gonads, internal and external genitalia into distinct male and female structures.

The process begins with gonad differentiation, which itself is tied developmentally back at the initial event of fertilization and the presence of either a Y or X chromosome in the sperm.

The endpoint of development could be considered the post-puberty active reproductive system. Interestingly, recent research is pointing to a link between neural and reproductive systems in how male and female brains may differentially develop under the influence of sex hormones and perhaps even the sex chromosomes.

There are 6 pages to work through in today's practical class, listed beside the small BGD icon at the top and bottom of each page.
Additional information sections are not part of the practical class content.

Genital Timeline

These are approximate timings and stages only.

24 days - intermediate mesoderm, pronephros primordium
28 days - mesonephros and mesonephric duct
35 days - uteric bud, metanephros, urogenital ridge
42 days - cloacal divison, gonadal primordium (indifferent)
49 days - paramesonephric duct, gonadal differentiation
56 days - paramesonephric duct fusion (female)
100 days - primary follicles (ovary)
postnatal 2 months of age - male primordial germ cells (gonocytes) are replaced by adult dark (Ad) and pale (Ap) spermatogonia forming the spermatogonial stem cell (SSC) population.

Textbooks

Hill, M.A. (2020). UNSW Embryology (20th ed.) Retrieved December 11, 2023, from https://embryology.med.unsw.edu.au

Historic Embryology - Genital
General: 1901 Urinogenital Tract \| 1902 The Uro-Genital System \| 1904 Ovary and Testis \| 1912 Urinogenital Organ Development \| 1914 External Genitalia \| 1921 Urogenital Development \| 1921 External Genital \| 1942 Sex Cords \| 1953 Germ Cells \| Historic Embryology Papers \| Historic Disclaimer
Female: 1904 Ovary and Testis \| 1904 Hymen \| 1912 Urinogenital Organ Development \| 1914 External Genitalia \| 1914 Female \| 1921 External Genital \| 1927 Female Foetus 15 cm \| 1927 Vagina \| 1932 Postnatal Ovary
Male: 1887-88 Testis \| 1904 Ovary and Testis \| 1904 Leydig Cells \| 1906 Testis vascular \| 1909 Prostate \| 1912 Prostate \| 1914 External Genitalia \| 1915 Cowper’s and Bartholin’s Glands \| 1920 Wolffian tubules \| 1935 Prepuce \| 1935 Wolffian Duct \| 1942 Sex Cords \| 1943 Testes Descent \| Historic Embryology Papers \| Historic Disclaimer

Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders. (links only function with UNSW connection)

Chapter 12 Urogenital System

Schoenwolf, G.C., Bleyl, S.B., Brauer, P.R., Francis-West, P.H. & Philippa H. (2015). Larsen's human embryology (5th ed.). New York; Edinburgh: Churchill Livingstone.(links only function with UNSW connection)

Chapter 15 Development of the Urinary System

Chapter 16 Development of the Reproductive System

Nussey, S and Saffron Whitehead, S. Endocrinology: An Integrated Approach. Oxford: BIOS Scientific Publishers; 2001.

Chapter 6 The gonad

Glossary Links

Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link

Cite this page: Hill, M.A. (2023, December 11) Embryology BGDB Practical - Sexual Differentiation. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/BGDB_Practical_-_Sexual_Differentiation

What Links Here?